Carrier aggregation (CA) means that a quantity of carriers used in a communication process is not limited to only one, and communication is performed simultaneously on one primary component carrier and several secondary component carriers. Cells in which UE that has a carrier aggregation function aggregates are classified into one primary cell and several secondary cells.
In the prior art, user equipment (UE) usually reports channel status information (CSI) of all cells to a base station by using a physical uplink control channel (PUCCH) of a primary cell. Specifically, when the UE receives, at a subframe N, a secondary cell activation command sent by the base station, the UE starts at a preset time (N+8) to send a CSI report carrying CSI of an activated secondary cell to the base station. For an inactive secondary cell, a time at which the UE obtains valid CSI may vary with tracking states of the inactive secondary cell by the UE. It is possible that the UE has not obtained a valid CSI measurement value for a CSI report in the beginning of the preset time. In this case, the UE needs to fill the CSI with a special measurement value, so as to inform the base station that the UE has not obtained a valid measurement value. The UE does not start to fill a normal CSI measurement value until the UE starts to obtain a valid CSI measurement value.
Because CSI of all cells are reported to a base station by using a PUCCH of a primary cell, PUCCH loads of the primary cell are excessively high. Therefore, introduction of a PUCCH to a secondary cell is currently discussed in 3GPP, so that some secondary cells report CSI reports to a base station by using the PUCCH of a secondary cell. However, the secondary cell to which a PUCCH is introduced may be in an inactive state. In this case, it cannot be ensured that the secondary cell starts CSI reporting at a preset time. Therefore, reliability of a system is decreased.